1. Field of the Invention
The present invention relates to a piezoelectric resonator supporting structure and a piezoelectric component including the same, and more particularly to a piezoelectric resonator supporting structure for supporting a piezoelectric resonator on a supporting member, such as a base, via a fixing member.
2. Description of the Related Art
FIG. 21 illustrates an example of a piezoelectric resonator relating to a background of the invention and to which the present invention is applied. FIG. 22 is a plan view showing a state in which insulating films are formed on a substrate of the piezoelectric resonator. The piezoelectric resonator 10 shown in FIG. 21 includes a rectangular parallelopiped substrate 12 which is 4 mm long, 1 mm wide, and 1 mm high. The substrate 12 includes twenty piezoelectric layers 14 that are stacked on each other and formed of, for example, piezoelectric ceramic material. These piezoelectric layers 14 have the same dimensions. As indicated by the arrows in FIG. 21, the piezoelectric layers 14 are polarized in a longitudinal direction of the substrate 12 such that the polarization directions of adjacent piezoelectric layers 14 are opposite to each other. The piezoelectric layers 14 at both ends of the substrate 12 are not polarized.
Internal electrodes 16 are disposed between piezoelectric layers 14 of the substrate 12, extend perpendicular to the longitudinal direction of the substrate 12 and are separated from each other in the longitudinal direction of the substrate 12. The internal electrodes 16 are arranged to cover the entire main surfaces of the piezoelectric layers 14. Therefore, the internal electrodes 16 are exposed at four side surfaces of the substrate 12.
A groove 17 is formed in a center portion, in a widthwise direction of the substrate 12, of one of the side surfaces of the substrate 12. At one of the portions, in the widthwise direction of the substrate 12, of the one side surface of the substrate 12 where the groove 17 is not formed, ends of alternate internal electrodes 16 are disposed so as to be covered with insulating films 18. Ends of other alternate internal electrodes 16 are disposed at the other of the portions, in the widthwise direction of the substrate 12, of the one side surface of the substrate 12 where the groove 17 is not formed.
At the one portion of the one side surface of the substrate 12, an external electrode 22 is disposed on, for example, the insulating films 18 provided on the alternate electrodes 16 so as to be connected to the alternate electrodes 16 provided on the other portion. At the other portion of the one side surface of the substrate 12, an external electrode 24 is disposed on, for example, the insulating films 20 provided on the alternate electrodes 16 so as to be connected to the alternate electrodes 16 provided on the one portion.
In the piezoelectric resonator 10 shown in FIG. 21, the external electrodes 22 and 24 are used as input/output electrodes. Since electric fields are applied between the internal electrodes 16 of adjacent layers when a signal is applied to the external electrodes 22 and 24, the piezoelectric layers 14, excluding those at both ends of the substrate 12, become piezoelectrically active. In this case, electrical fields opposite in direction are applied to the piezoelectric layers 14 of the substrate 12 that are polarized in opposite directions. Therefore, the piezoelectric layers 14 as a whole tend to expand and contract in the same direction. In other words, when alternating current electric fields in the longitudinal direction of the substrate 12 are applied to the individual piezoelectric layers 14 by the internal electrodes 16 and the internal electrodes 16 connected to the external electrodes 22 and 24, so that a driving force that expands and contracts the individual piezoelectric layers 14 is generated thereat, the entire piezoelectric resonator 10 is excited with a fundamental vibration of a longitudinal vibration, with the center portions, in the longitudinal direction of the substrate 12, of the substrate 12 acting as nodes.
A description will now be provided of a conventional piezoelectric component in which the piezoelectric resonator 10 shown in FIG. 21 is mounted via fixing members on a base which defines a supporting member.
FIG. 23 illustrates a state before the piezoelectric resonator of the conventional piezoelectric component is fixed. FIG. 24 illustrates a state after the piezoelectric resonator of the piezoelectric component has been fixed. The piezoelectric component 1 shown in FIGS. 23 and 24 includes a base 2 defining a supporting member. Two pattern electrodes 3 are provided on the base 2. Fixing members 4 made of a urethane-type electrically conductive material, that is, a urethane-type synthetic resin containing 85 wt % of Ag are provided on respective center portions, in the longitudinal direction of the external electrodes 22 and 24, of the external electrodes 22 and 24. The fixing members 4 are bonded to the two pattern electrodes 3 on the base 2 via an electrically conductive paste 5 made of an epoxy-type electrically conductive material, that is, an epoxy-type synthetic resin containing Ag. This causes the external electrodes 22 and 24 of the piezoelectric resonator 10 to be electrically coupled to the respective pattern electrodes 3 on the base 2, through the respective fixing members 4, whereby the piezoelectric resonator 10 is fixed to the base 2 through the fixing members 4.
In this case, the larger dimension W1 of the upper portion of each fixing member 4 of the piezoelectric resonator 10 is in the longitudinal direction thereof, the easier it is for vibration to be transmitted. The dimension W1 is in the range of from 1.0 mm to 1.4 mm.
The relationship between the transmission of vibration and dimension W2 of the lower portion of each fixing member 4 of the piezoelectric resonator 10 in the longitudinal direction thereof is small, but with regard to the strength with which the base 2 and the fixing members 4 are grounded, it is, for example, set equal to or greater than 0.5 mm.
Although the amount of vibration transmitted varies with the hardness of the fixing members 4 and the amount of Ag contained in the fixing members 4, it can be reduced by a certain amount even in a direction of thickness of the fixing members 4 by thickness t1 of the fixing members 4. The larger the value of thickness t1, the smaller the amount of vibration transmitted. The thickness t1 has an upper limit due to the height of the piezoelectric components produced. It is within a range of, for example, from 130 xcexcm to 170 xcexcm.
Although thickness t2 (shown in FIG. 23) prior to bonding with the electrically conductive paste 5 is not directly related to the transmission of vibration, when the electrically conductive paste 5 is thick, the fillet size with respect to the fixing members 4 becomes large, thereby increasing the amount of vibration transmitted. On the other hand, when it is thin, the strength with which the fixing members 4 is grounded is reduced. Therefore, the thickness t2 is in a range of from 35 xcexcm to 55 xcexcm.
The piezoelectric component 1 shown in FIGS. 23 and 24 possess the impedance characteristics and the phase characteristics illustrated in FIG. 25 and the filter characteristics illustrated in FIG. 26.
However, in the above-described conventional piezoelectric component 1, when the dimension W1 of the upper portion of each fixing member 4 is made smaller in order to restrict the transmission of vibration, the dimension W2 of the lower portion of the fixing members 4 inevitably becomes small, so that sufficient supporting strength cannot be obtained. On the other hand, in order to make the dimension W2 of the lower portion of the fixing members 4 equal to or greater than a specification value that is equal to or greater than 0.5 mm, the dimension W1 of the upper portion of the fixing members 4 becomes equal to or greater than 0.9 mm, making it easier for vibration to be transmitted.
In addition, in the above-described conventional piezoelectric component 1, when the thickness t1 of the fixing members 4 is made large in order to restrict the transmission of vibration, the manufactured piezoelectric component 1 becomes taller, so that the goal of making light, thin, short, small piezoelectric components cannot be achieved. Further, there has been an increasing demand for decreasing the maximum height of current products from 1.9 mm to 1.7 mm or 1.5 mm, so that the fixing members 4 are becoming shorter and shorter, making it necessary to investigate ways to reduce the amount of energy transmitted.
Still further, in the above-described conventional piezoelectric component 1 having the above-described structure and dimensions, in order to restrict the transmission of vibration, it is necessary to improve the materials used for the fixing members 4 and the electrically conductive paste 5. An effective lower Young""s modulus cannot be obtained due to strength requirements and poor cutting performance during cutting of a piezoelectric resonator or cutting operations carried out using a dicing machine. Still further, since it is clear that vibration is transmitted through Ag fillers in the fixing members 4, the amount of vibration transmitted can be restricted by reducing the amount of Ag. However, since, in order to ensure electrical conduction, current electrically conductive pastes are based on urethane-type synthetic resin, the amount of Ag contained cannot be reduced to an amount that is 80 wt % or less.
To overcome the above described problems, preferred embodiments of the present invention provide a piezoelectric resonator supporting structure which can restrict the amount of vibration transmitted from a piezoelectric resonator to a supporting member while maintaining the strength with which the piezoelectric resonator is held by the supporting member; and a piezoelectric component including the same.
One preferred embodiment of the present invention provides a piezoelectric resonator supporting structure for supporting a piezoelectric resonator on a supporting member via a fixing member, the piezoelectric resonator being adapted to be vibrate in a longitudinal vibration mode, wherein at least a portion of the fixing member that contacts the piezoelectric resonator is made of a vibration transmission restricting material for restricting transmission of vibration from the piezoelectric resonator to the supporting member through the fixing member.
In such a piezoelectric resonator supporting structure of this preferred embodiment of the present invention, the portion of the fixing member that contacts the piezoelectric resonator may correspond to, for example, an outside portion or an inside portion of the fixing member.
In such a piezoelectric resonator supporting structure, a portion of the fixing member which extends from the portion of the fixing member that contacts the piezoelectric resonator to a portion of a portion of the fixing member at the supporting member side may be formed of the vibration transmission restricting material.
In such a piezoelectric resonator supporting structure, the vibration transmission restricting material may include urethane or silicone.
Another preferred embodiment of the present invention provides a piezoelectric component including any one of the above-described piezoelectric resonator supporting structures, wherein the supporting member is a base and a cover is provided on the base so as to cover the piezoelectric resonator.
In such a piezoelectric component, a plurality of the piezoelectric resonators may be provided.
In such piezoelectric resonator supporting structures and piezoelectric components including the same, a portion of the fixing member that contacts the piezoelectric resonator is formed of a vibration transmission restricting material, making it possible to restrict the transmission of vibration from the piezoelectric resonator to the supporting member while maintaining the strength with which the piezoelectric resonator is held by the supporting member.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.